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sys: util: provide bitfield construction/extraction utility macros

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Those are especially useful with hardware device registers.
They behave the same way as their Linux equivalent, with a much
simpler implementation for now.

Example:

 #define REG_FIELD_A  GENMASK(6, 0)
 #define REG_FIELD_B  BIT(7)
 #define REG_FIELD_C  GENMASK(15, 8)
 #define REG_FIELD_D  GENMASK(31, 16)

Get:
 a = FIELD_GET(REG_FIELD_A, reg);
 b = FIELD_GET(REG_FIELD_B, reg);

Set:
 reg = FIELD_PREP(REG_FIELD_A, 1) |
       FIELD_PREP(REG_FIELD_B, 0) |
       FIELD_PREP(REG_FIELD_C, c) |
       FIELD_PREP(REG_FIELD_D, 0x40);

Modify:
 reg &= ~REG_FIELD_C;
 reg |= FIELD_PREP(REG_FIELD_C, c);

Signed-off-by: Nicolas Pitre <npitre@baylibre.com>
This commit is contained in:
Nicolas Pitre 2021-09-07 23:40:24 -04:00 committed by Anas Nashif
parent aeee57bfe1
commit bd73cd5512
1 changed files with 16 additions and 0 deletions
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16
include/sys/util.h
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@ -58,6 +58,22 @@ extern "C" {
#define GENMASK(h, l) \
(((~0UL) - (1UL << (l)) + 1) & (~0UL >> (BITS_PER_LONG - 1 - (h))))
/** @brief Extract the Least Significant Bit from @p value. */
#define LSB_GET(value) ((value) & -(value))
/**
* @brief Extract a bitfield element from @p value corresponding to
* the field mask @p mask.
*/
#define FIELD_GET(mask, value) (((value) & (mask)) / LSB_GET(mask))
/**
* @brief Prepare a bitfield element using @p value with @p mask representing
* its field position and width. The result should be combined
* with other fields using a logical OR.
*/
#define FIELD_PREP(mask, value) (((value) * LSB_GET(mask)) & (mask))
/** @brief 0 if @p cond is true-ish; causes a compile error otherwise. */
#define ZERO_OR_COMPILE_ERROR(cond) ((int) sizeof(char[1 - 2 * !(cond)]) - 1)